From: Paul Winalski <paul.winalski@gmail.com>
To: coff@tuhs.org
Subject: [COFF] Re: Terminology query - 'system process'?
Date: Fri, 15 Dec 2023 12:51:47 -0500 [thread overview]
Message-ID: <CABH=_VTV+ypgEVvbRTNwxC5os_2PuZLXJPSB0ai8n7r_-tQXbA@mail.gmail.com> (raw)
In-Reply-To: <4416CB1B-CDE2-42DA-92F2-33284DB6093F@iitbombay.org>
For me, the term "system process" means either:
o A conventional, but perhaps privileged user-mode process that
performs a system function. An example would be the output side of a
spooling system, or an operator communications process.
o A process, or at least an address space + execution thread, that
runs in privileged mode on the hardware and whose address space is in
the resident kernel.
Do Unix system processes participate in time-sliced scheduling the way
that user processes do?
On 12/14/23, Bakul Shah <bakul@iitbombay.org> wrote:
>
> Exactly! If blocking was not required, you can do the work in an
> interrupt handler. If blocking is required, you can't just use the
> stack of a random process (while in supervisor mode) unless you
> are doing some work specifically on its behalf.
>
>> Interestingly, other early systems don't seem to have thought of this
>> structuring technique.
>
> I suspect IBM operating systems probably did use them. At least TSO
> must have. Once you start *accounting* (and charging) for cpu time,
> this idea must fall out naturally. You don't want to charge a process
> for kernel time used for an unrelated work!
The usual programming convention for IBM S/360/370 operating systems
(OS/360, OS/VS, TOS and DOS/360, DOS/VS) did not involve use of a
stack at all, unless one was writing a routine involving recursive
calls, and that was rare. Addressing for both program and data was
done using a base register + offset. PL/I is the only IBM HLL I know
that explicitly supported recursion. I don't know how they
implemented automatic variables assigned to memory in recursive
routines. It might have been a linked list rather than a stack.
I remember when I first went from the IBM world and started
programming VAX/VMS, I thought it was really weird to burn an entire
register just for a process stack.
> There was a race condition in V7 swapping code. Once a colleague and I
> spent two weeks of 16 hour debugging days!
I had a race condition in some multithread code I wrote. I couldn't
find it the bug. I even resorted to getting machine code listings of
the whole program and marking the critical and non-critical sections
with green and red markers. I eventually threw all of the code out
and rewrite it from scratch. The second version didn't have the race
condition.
-Paul W.
next prev parent reply other threads:[~2023-12-15 17:51 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-14 23:29 Noel Chiappa
2023-12-14 23:54 ` Larry McVoy
2023-12-15 1:15 ` Bakul Shah
2023-12-15 17:51 ` Paul Winalski [this message]
2023-12-15 18:08 ` Warner Losh
2023-12-16 2:04 ` Greg 'groggy' Lehey
2023-12-16 19:21 ` Paul Winalski
2023-12-16 19:44 ` Paul Winalski
2023-12-15 13:43 ` Dan Cross
2023-12-19 13:54 ` Derek Fawcus via COFF
-- strict thread matches above, loose matches on Subject: below --
2023-12-20 20:35 Noel Chiappa
2023-12-20 19:31 Noel Chiappa
2023-12-20 20:29 ` Paul Winalski
2023-12-31 3:51 ` steve jenkin
2023-12-14 21:48 [COFF] " Noel Chiappa
2023-12-14 22:06 ` [COFF] " Bakul Shah
2023-12-14 22:12 ` Warner Losh
2023-12-14 22:09 ` Clem Cole
2023-12-15 14:20 ` Dan Cross
2023-12-15 16:25 ` Warner Losh
2023-12-15 17:13 ` Bakul Shah
2023-12-15 6:24 ` Lars Brinkhoff
2023-12-15 18:30 ` Stuff Received
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